What it is!!!!

Hey guys,
Help me out here.
I have 3000 miles on my new engine but my speedo is off by 7 mph to fast.
So if I am going 60mph I am really going 53mph.
So the question is how many miles do I really have on my new engine.
Thanks in advance,
Schoon

I'm not sure on this,........but I'll take a shot.
53 is roughly 88% of 60.
I took the remaining 12% X 3000 and came up with 360 miles, subtract this from 3000,
.... I figure 2640 total miles.
(corrections appreciated)

I believe, that would be correct, or I should say is correct if you were traveling 60mph ALL the time. However, you'll find that your speedometer is off less the slower you go. So when your doing 35 it may be only 3 mph off, or less. in other words if you drive 7 mph it's not reading "0" is it?
Hey this would be a good one to present to my Engineering department,

Gorich is correct. However, if you divide 3000 by 1.07 you arrive at 2803.7383 miles, if you ALWAYS drove @ 60 mph

quote:

ORIGINAL: Doctor K

Gorich is correct. However, if you divide 3000 by 1.07 you arrive at 2803.7383 miles, if you ALWAYS drove @ 60 mph

As my math teacher always said, "show your process".
Where did ya get the 1.07?

I compute 13% error - the actual speed is 53 mph and the error is 7 mph. 7/53 = 13%.
Speedometers are often a bit optimistic, but this is rather extreme.

But regardless, I would not assume that, because the speedometer needle is that far off, the odometer is also that far off. This much error could be because of some mis-assembly or malfunction or miscalibrationin the speedo or its needle.

If it were my car, I would test the odometer. Find a ten mile stretch of highway with mile markers. Note the mileage to the tenth just as you pass a marker and drive at 60 or so (it really should not matter what speed) for ten miles, then note as you pass mile marker #10 how far your odometer says you have gone, if it has the same 13% over error it will say around 11.3 miles traveled rather than 10.

A thought, not knowing the details of the car: if an automatic transmission vette had the ECM programmed for the wrong axle ratio, for 2.73 while the car actually had the 3.15 rear axle ratio, it would have a bit over a 14% error: showing 60 mph when actually doing just under 52 -- just a bit more error than you have measured -- it would be easy to be off by that small difference and not know it. If your odometer test shows you are off that much, I would look at whether the ECM (if this is a newer vette) or the speedometer cable gear (if older), is incorrect for the axle ratio.

it's clocking 1.1320 miles for every one mile travled. 60/53=1.1320 3000/1.1320=2650.1766 is that right?

Nice explanation Lee
I let my Engineers ponder over this one, and just like the true Engineers they are they couldn't figure it ou!
 

I used to work with Engineers, when I worked on the railroad, they ain't so smart!

In addition to what Lee pointed out it could have something to do with tire size also or a comination of things. hope you figure it out. do the Highway patrole still check speedos for people or have a shop that does their cars?

Just a thought here, I am not an engineer, just a Land Surveyor. But, no matter what speed you were going, wouldnt the error be the same? I mean, you wouldnt see it on the speedo because as richb said, its not reading 0 if you are going 7. But, assuming the error at 100mph is 12mph, then that would mean starship is correct and that it is 88% accurate. which means when it read 50mph, it would only be about 44mph. And then you just keep working down from there. So the slower he got he wouldnt notice it right? I kinda went off on a rant there, but the point of that was to say that no matter how fast he was going, the Odometer would still be off the same amount, it would just be carried out. So whoever figured up the original number of what his Odometer should say, they are probably right ASSUMING we have all of the information correct.
 
Im probably wrong though!
 
Matt

quote:

ORIGINAL: 94blackC4

Just a thought here, I am not an engineer, just a Land Surveyor. But, no matter what speed you were going, wouldnt the error be the same? I mean, you wouldnt see it on the speedo because as richb said, its not reading 0 if you are going 7. But, assuming the error at 100mph is 12mph, then that would mean starship is correct and that it is 88% accurate. which means when it read 50mph, it would only be about 44mph. And then you just keep working down from there. So the slower he got he wouldnt notice it right? I kinda went off on a rant there, but the point of that was to say that no matter how fast he was going, the Odometer would still be off the same amount, it would just be carried out. So whoever figured up the original number of what his Odometer should say, they are probably right ASSUMING we have all of the information correct.

Im probably wrong though!

Matt

 
I believe you're right, the diff would remain constant. Otherwise, all speedos would be inaccurate no matter how they were set.

Coffee is coming out of my nose.  Steam is coming out of my ears.  My CF friends have all gone off of their rockers with the cold weather approaching!!!  How *DARE* anyone in this forum reccomend driving your C3 for any distance even *approaching* ten miles at a measly 60 MPH.  The cops should pull you over and impound your Vette if you even consider doing a silly stunt like that on the public roads!!

Merry Xmas
bill.

quote:

ORIGINAL: wrwalke


Coffee is coming out of my nose.  Steam is coming out of my ears.  My CF friends have all gone off of their rockers with the cold weather approaching!!!  How *DARE* anyone in this forum reccomend driving your C3 for any distance even *approaching* ten miles at a measly 60 MPH.  The cops should pull you over and impound your Vette if you even consider doing a silly stunt like that on the public roads!!

Merry Xmas
bill.

Whoa......bill.......I didn't condone drivin' a C3 at 60 mph! I just used the figure for math's sake!
How's this,...........
88% of 120 mph, 12% of 3000!
Is that better?

I would not assume that the error is constant as a function of speed, or that it affects the oidometer the same as the speedometer, until proven.  If so, that is a big clue to the problem (my first suspect then is the gear ratio correction in the ECM).  If it varies as a function of speed then it is almost certainly a flaw in the speedometer mechanism itself as opposed to the sensors and electrical system.

Aha!! Lee Willis is correct. I wasnt thinking about that! I was just ASSUMING that the problem would be the gear ratio. The gear ratio and tire size (as programmed into the ECM), i believe, would be the only two things that would make the difference consitent. If it isnt either of those problems, then we can scrap whatever I said. I dont believe tire size would affect the speedo 7mph. So the only other option for my theorum would be the gear ratio.
 
Hey SCHOON, do you have stock gears or are they aftermarket? If they are aftermarket, when you got your motor rebuilt, did they return the ECM to the stock settings? If so, your speedo could be off because of that and that would also help us figure out what the deal is with how many miles you have actually put on it.
 
Matt